Worm pumps using rotors which have the configuration of a helix, i.e. a screw configuration and of a uniform circular cross section over the pumping length of the worm with the circular cross section being offset from the axis of rotation of the eccentric worm rotor by a certain eccentricity, are known. The rotor is displaceable in a stator chamber and generally the pump medium flows directly through this chamber being displaced by the rotation of the pump. Worm pumps of this type are described by Hartinger, Taschenbuch der Abwasserbehandlung, Band 2, Carl Hanser Verlag, 1977 (Handbook of Sewage Treatment, Volume 2, Carl Hanser Publishing, 1977). In such pumps the stator generally has screw-like recesses with twice the pitch and number of helices as the eccentric worm rotor. The rotation axis of the eccentric worm rotor and the longitudinal axis of the stator chamber are offset by the eccentricity of the eccentric worm rotor.
This pump has been found to be expensive to fabricate and the drive system for the pump is relatively complex and expensive as well. Since the motion is relatively complex, reliability is often in question. The pump stator, against which the rotor must seal directly, is subject to considerable wear. The materials from which the pump stator and the rotor are made must be determined based upon resistance to attack by the material pumped. The prior art pump, moreover, can be traversed by only one liquid stream, i.e. per rotor/stator pair only a single flowable substance can be displaced.